Phosphorylation of AMPA-type glutamate receptors (AMPARs) may be important for learning and memory in the hippocampus. AMPARs are ligand-gated ion channels responsible for most excitatory neurotransmission in the brain, and changes in phosphorylation of these receptors alter synaptic transmission, leading to synaptic plasticity. In particular, phosphorylation of residues on the C-terminus of the AMPAR GluRI subunit is under intense study. When these residues are phosphorylated, signaling through AMPARs is enhanced;thus therapeutics targeting these sites could improve cognitive deficits in humans. Additionally, altering phosphorylation of GluR1 may be important in treating mood disorders such as depression and bipolar disease. Importantly, a novel phosphorylation site on GluR1 has been recently uncovered and little is known about its functional significance. This residue, threonine 840 (T840), appears to have a role in hippocampal synaptic plasticity and may modulate phosphorylation of other sites on the C- terminus of GluRI. Thus, T840 may have a crucial role in learning and memory. In order to determine the importance of T840 phosphorylation in synaptic plasticity, we will investigate: 1. The molecular mechanisms of T840 phosphorylation: We will treat acute hippocampal brain slices and hippocampal cultures with different pharmacological and molecular reagents, and measure changes in T840 phosphorylation using immunoblotting to test our hypothesis that T840 is an important target for protein kinases and protein phosphatases known to have roles in synaptic plasticity. 2. The functional significance of T840 phosphoryation: We will first use whole-cell recordings in HEK cells transfected with GluRI to investigate our hypothesis that T840 phosphorylation influences the biophysical properties of the receptor. Second, we will test our hypothesis that phosphorylation at this site may regulate phosphorylation at nearby sites on the C-terminus of GluRI by using both whole-cell electrophysiology and immunoblotting of transfected hippocampal neurons and HEK cells. Relevence of Research to Public Health: The experiments outlined in this proposal are directly relevent to the mission of the NIMH because they will provide insight into the cellular processes in the hippocampus, a brain region crucial to learning and memory. This information can be used to determine the changes in hippocampal function underlying cognitive and mood disorders, and possibly lead to the discovery of more effective targeted therapies.